FEP (fluorinated ethylene propylene) resins such as Dupont FEP are produced by co-polymerization of tetrafluoroethylene and hexafluoropropylene and have predominantly linear chains.

FEP has a crystalline melting point of 554 degrees Fahrenheit, though its mechanical properties are suitable from cryogenic to about 400 degrees Fahrenheit. It is a soft plastic with lower tensile strength, wear resistance, and creep resistance than many other engineering plastics.

FEP fluoropolymer can be compounded in almost a limitless array of thermoplastic, for increasing load bearing capacity, reduced friction, higher mechanical strengths, improved thermal properties, and greater endurance. Non stick (release) and chemical protection characteristics are outstanding.

FEP differs from other Dupont Teflon or PTFE (polytetrafluoroethylene) resins in that it is melt-processable, much like PFA, though PFA can be used at even higher temperatures.
FEP coatings are highly resistant to oxidation and action of chemicals including strong acids, alkali, oxidizing agents, nuclear radiation, UV rays, and ozone.

Absorption rates are comparatively much lower with FEP plastic than almost all others. It absorbs practically no common acids or bases at temperatures as high as 400 degrees Fahrenheit. Weight increases are generally less than 1% when exposed at elevated temperatures for long periods. Aqueous solutions are absorbed little. Moisture absorption is typically less than 0.01% at ambient temperature and pressure.

Gases and vapors, too, show low permeation rates with FEP than for other thermoplastics. In general, permeation increases with temperature, pressure, and surface area contact, but decreases with increased thickness.

Mechanical properties include, but are not limited to, flexibility at low temperatures, stability at high temperatures, low coefficient of friction, dielectric strength, corrosion resistance, and non stick (release).

There have been many practical non-lubricated mechanical systems developed with coefficient of friction as low as 0.05-0.08. Even at higher dynamic PV (8,000 to 10,000) coefficient of friction around 0.10 or less is feasible.

Dupont FEP resins exhibit exceptionally low friction in non-lubricated environments, especially at low surface velocities and pressures higher than 5 pounds per square inch. The coefficient of friction actually increases with sliding speed up to 100 feet per minute, under all pressure conditions. It’s this phenomena that prevents ‘stick-slip’ tendencies. In addition, no ‘squeaking’ or noise occurs, even at the highest speeds. Above 150 feet per minute, sliding velocity has little effect (on friction) at combinations of pressure and velocity below the composition’s PV limit. Static friction decreases with increasing pressure.

PV limits define the maximum combinations of pressure and velocity at which these materials will operate continuously without lubrication. PV limits for non-reinforced FEP approach zero at temperatures near 400 degrees Fahrenheit. However, useful PV limits must take into account the composition’s wear characteristics and allowable wear for the application.

When considering Dupont products or FEP in non stick applications, you must sometimes consider creep and cold flow. Generally, a plastic material subjected to continuous load experiences a continued deformation with time called creep or cold flow. Deformation can be significant, even at room temperature or below; hence, the name ‘cold flow’.

Creep is the total deformation under stress after a specified time in a given environment beyond that instantaneous strain which occurs immediately upon loading. Independent variables affecting creep are time under load, temperature, and load or stress level.

As long as the stress level is below the elastic limit of the material, performance is sustainable. And beyond a certain point, creep is small and may be neglected for many applications. In many cases, too, there is compressive recovery from various percentages of strain. Nearly complete where the original strain does not exceed the yield strain.

FEP comes from relatively newer fluorocarbon resin products. It is especially important for designers and end-users requiring release (non stick) performance or chemical stability.

Tensile strength, stiffness, and flexural modulus are outstanding. Both at cryogenic and higher continuous temperatures (400 F).